Presentation on theme: "CH: 10 THE VITAL ROLE OF WATER ON EARTH – ONE OF THE MOST IMPORTANT INGREDIENTS FOR LIFE ! By: Ms. Thompson."— Presentation transcript:

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W HAT YOU WILL LEARN... You will... Describe the distribution of water on Earth Illustrate the water cycle Explain how water shapes the landscapes (stay tuned for Ms. Thompsons travel photos )

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D ISTRIBUTION OF WATER : 70% OF THE SURFACE IS COVERED IN WATER Use a pie graph to illustrate your understanding of the distribution of water on Earth. About 97% of this water is found in oceans Only 3% of the planets water is fresh water. About 1% of that is available to us as fresh water.

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E ND D ISCUSSION Q UESTIONS Explain what would happen to the water cycle if the oceans covered only 25% of the planet. A lot less water would be evaporating; therefore, there would be a lot less water moving through the cycle (e.g., less precipitation to refill water supplies). Explain why you feel cold after coming out of a warm swimming pool on a hot, sunny day. (Hint: think of water and the transfer of heat). The water absorbs heat as it evaporates. It takes some of the heat from your body. As the water evaporates, it makes your skin feel cold.

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MAGIC EGG http://www.youtube.com/watch?v=f2H3xsTR7rg&feature=endscre en&NR=1 When an egg is placed in fresh water, it doesnt displace enough water, and is more dense than the water around it. This creates unbalanced forces that send the egg to the bottom of the cup. Adding salt, causes the salt crystals to break down into molecules and fill the space between the water molecules. The solution now has more mass in the same volume which changes the density of the water. When you add an egg it still displaces the water, but now floats instead of sinking.

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FRESH VS. SALT WATER Sodium ions (Na +) and chloride ions (CI-) add up to more than 85% of all the dissolved solids in the ocean. When combined, they form a compound call sodium chloride (NaCI)- SALT Salt water differs from fresh water in several major ways. The main one is in its salinity. This characteristic gives ocean water a different density, freezing point, and boiling point than fresh water. Even though salt water and fresh water are connected, they play different roles in the water cycle.

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A REAS OF SALINITY Salt deposits are left behind when evaporation and freezing occurs. Equator : greater salt North and South Poles : greater salt Near coastlines : less salt and diluted.

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FREEZING POINT Adding salt disrupts the equilibrium. The salt molecules dissolve in the water, but do not attach easily to the solid ice. There are fewer water molecules in the liquid because some of the water has been replaced by salt. This means that the number of water molecules able to be captured by the ice (frozen) goes down, so the rate of freezing goes down. The rate of melting of the ice is unchanged by the presence of the salt, so melting is now occurring faster than freezing. So the ice eventually melts.

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FREEZING POINT CONT. In order to return the system to equilibrium, where the number of molecules of water that are freezing is equal to the number of ice molecules that are melting (this is the freezing/melting point ), we must lower the temperature sufficiently to make the water molecules slow down enough so that more can attach themselves to the ice. In our example, this point is reached at -4°C, which would be the new freezing/melting point. The higher the concentration of salt, the lower the freezing point drops.

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BOILING POINT Why do you add salt to water? Aside from flavour, salt is added to water because it increases the boiling point of the water, meaning your water will have a higher temperature when you add the pasta, so it will cook better. That's how it works in theory. In reality, you would need to add 230 grams of table salt to a liter of water just to raise the boiling point by 2° C. That is much more salt than anyone would care to have in their food.

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The Dead Sea is not really a sea, it is actually a land locked lake between Israel and Jordon. Since there is no outlet, the water in the Dead Sea evaporates depositing the dissolved minerals, and since it has no place to go, the dissolved salt minerals continue to accumulate and be concentrated in the sea.

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DEAD SEA FACTS The extreme salinity of the water excludes any animal or vegetable life. 8.6 times saltier than the ocean and one of the worlds saltiest bodies of water. 417 meters below sea level and lowest point of earth surface

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SOURCES OF FRESH WATER Water makes its long journey back to the ocean, pulled along by gravity. The flow is called run-off. The amount of run-off can lead to the flooding of surrounding land and washing away top soil from fields. Fast moving rivers can also be harmful to aquatic animals. Run-off is affected in the following ways - Nature of the ground material: rock versus soil - Amount of rain: saturated grounds= increase in run-off as the ground can not absorb any more. - Length of rain: saturation leads to run-off - Slope of land: steeper land= faster run-off, and less absorption - Amount of vegetation: little vegetated areas will have a greater amount of run-off - Amount of development: developed areas will lead to an increase in run-off because the water is channelled into storm sewers.

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C ITES LISTED http://www.worsleyschool.net/science/files/saltan dfreezing/ofwater.html http://www.worsleyschool.net/science/files/saltan dfreezing/ofwater.html Salt and the freezing point of water website

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CAN ANY GOOD COME FROM A SEWER ? A microbe can be turned into a fuel cell. A microbial fuel cell could be developed to clean water at waste treatment plants, and generate modest amounts of electricity as a bonus.